As is well known, semiconductor wafers are scribed along specific lines and thereafter separated along such lines to divide the wafer into semiconductor chips. Such division lines can be scribed with a diamond-pointed scribing tool or cut by a laser or saw. However, when the lines are scribed or partially cut, the wafer is not immediately separated into its individual pieces but must be broken after scribing has occurred.
Many attempts have been made to provide apparatus for breaking a semiconductor wafer into individual pieces with each piece representing a particular semiconductor chip. For the most part, these attempts have been unsatisfactory for one or more reasons. Specifically, the yield of a wafer using conventional techniques has been relatively low, and the loss of a large number of semiconductor chips from a given wafer represents a large loss in profits which could be realized if the yield were greater.
Breaking a scribe line is implemented by putting it in tensile strain. The point or bottom of the vertical crack under the scribe line will start experiencing molecular bond failures; slowly at first and increasing in an avalanche fashion. When the bond failure becomes quite rapid, the strain energy required to feed the failing is minuscule in relation to the tensile strength of the material. When the rapid bond failure initiates, it commonly starts at the edge of the wafer. The strain induced around the unbroken scribe line is released as the scribe line starts to fail and supplies the necessary energy to feed the break along the scribe line.
Until this invention, all known breaking methods and apparatus applied the tensile breaking strain in a mass fashion; e.g. causing the wafer to conform to a convex cylindrical section parallel to the scribe lines, or causing a single scribe line to bend about an edge in a guillotine fashion. All of these techniques attempt to break a scribe line instantly. Since scribe lines always break in a serial fashion from point A to point B, not instantaneously, the strain energy built up in the material affects the completion of the break. Usually, this residual strain energy is too much and ill-applied to achieve a perfect break. The excess applied strain contributes to chipping, edge degradation and skew (off scribe line) breaks.
Additionally, the traditional breaking methods always touch the entire surface of the wafer. With the introduction of "air-bridge" circuits (very thin micro-conductors, suspended over other conductors with the air space between acting as an insulator), breaking wafers has become more difficult because the air bridges are very fragile and must not be touched or contaminated during the breaking operation. Because of the drawbacks associated with conventional breaking techniques, a need has continued to exist for some time for an improved breaking apparatus and method to permit high yields yet provide for simplicity in operation without interference with the scribing step. The present invention satisfies this need because not only does it apply a limited (and adjustable) strain just necessary to drive the bond failures along the scribe line, but it also integrates breaking with scribing and thus can locate breaking forces outside the active circuit areas, which is normally the wafer separation grid area.